- Organisms get rid of the gaseous wastes generated through respiration. But other metabolic activities that generate nitrogenous materials are removed by specialized organs.
- The process involved in the removal of these harmful metabolic wastes from the body is called excretion.
The main function of the excretory system is to remove the nitrogenous substances formed during metabolism process in human body.
- In unicellular organisms, these wastes are removed by process of diffusion from the body surface into the surrounding water.
- In multicellular organisms, specialized organs perform the process of excretion.
In humans, the main functional excretory organs are:
- Urinary Bladder
Other excretory organs in human body includes:
Kidney & its Function
- Kidneys are located in the abdomen, one on either side of the backbone.
- It is the main excretory organ in the human body.
- The outer part of kidney is called cortex. The inner part of the kidney is called medulla.
- The main function of kidney and the excretory system is purification of blood by filtering out the waste products like uric acid or urea from the blood.
- This filtration is performed by cluster of very thin-walled blood capillaries. It is the basic filtration unit in the kidneys.
- Each capillary cluster in the kidney is associated with the cup-shaped end of a coiled tube called Bowman’s Capsule.
- The process of filtration of liquids into the cavity of Bowman’s capsule is called ultra-filtration.
- Bowman’s capsule collects the filtrate i.e. the product left after the filtration.
- Each kidney has large number of filtration units called nephrons packed close together.
Function of Excretory System
- The main function of the excretory system is to filter out nitrogenous waste products like urea and uric acid from the blood plasma and then remove it from the body.
- Kidneys filter out the uric acid from the blood and send back the blood inside the body circulation. Kidney makes urine to filter out waste products from the blood.
- Urine is produced in the kidneys during filtration, then it passes through the ureters into the urinary bladder where it is stored until it is released through the urethra.
- Some substances like glucose, amino acids, salts and a major amount of water are selectively re-absorbed as the urine flows along the nephron, where filtration takes place.
- The amount of water re-absorbed depends on how much excess water there is in the body, and on how much of dissolved waste there is to be excreted. This is how the amount of urine produced is regulated by the excretory system.
- The urine forming in each kidney eventually enters a long tube, the ureter, which connects the kidneys with the urinary bladder.
- Urine is stored in the urinary bladder until the pressure of the expanded bladder leads to the urge to pass it our through the Urethra.
- The bladder is muscular, so it is under nervous control, as a result, we can usually control the urge to urinate.
Excretion in Plants
- Plants use completely different strategies for excretion than those of animals.
- Oxygen is the waste product generated during photosynthesis. This is released during the gaseous exchange that takes place through stomata.
- Plants also get rid of excess water through transpiration.
- For other wastes, plants use the fact that many of their tissues consist of dead cells, and that they can even lose some parts such as leaves.
- Many plant waste products are stored in cellular vacuoles.
- Plant also excrete some waste substances into the soil around them.
Did You Know
- The weight of each kidney is 140 grams.
- In kidneys, average 125 ml per minute blood is filtrated i.e. 180 litres per day.
- The colour of urine is yellow due to the presence of urochromes in it.
- Urine is acidic and its pH value is 6.